1. Field of the Invention
The present invention relates to a transmit-focusing and beam-forming apparatus and method in an ultrasonic imaging system. In particular, the invention relates to an apparatus for transmit-focusing and beam-forming and the method thereof, which forms adaptive scan-line data by applying a plurality of delay profiles.
2. Description of the Related Art
As well known in the related art, an ultrasonic imaging system adopting a phased array includes array of a plurality of transducers. Conventional transmit-focusing and beam-forming apparatuses are shown in FIG. 1A and FIG. 1B respectively. As shown in FIG. 1, these systems include a plurality of channels, and each channel includes transmitting and receiving units connected to each of the transducers. The transducers of the transmitting unit fire a group of ultrasonic pulses into a target object, for instance, a human body. In order to focus the transmitted ultrasonic energy on a predetermined point, a delay profile of the ultrasonic pulses is determined in a way that the transmitted pulses interfere each other positively at the predetermined point, and each transducer outputs pulses according to the predetermined delay profile at a proper time.
Referring to FIG. 1A, a process of generating the ultrasonic pulses according to the conventional technology is explained. First, when a trigger pulse informs the start of transmitting the ultrasonic pulses, each of delay circuits 1 applies an appropriate transmitting delay to each of the transducer elements of the transmitting unit. Setting the applied delay as a starting point, transmitting waveforms are read from waveform table 3 and amplified by power amplifier 5. Amplified pulses are provided to each of the transducer elements and the ultrasonic pulses are transmitted.
These pulses are reflected by materials and return to the transducer array 10. The ultrasonic image is generated by beam-forming the reflected signals. Referring to FIG. 1B, a beam-forming of the reflected signals is explained.
The ultrasonic energy reflected off the target object returns to each array device with a time variation. The received signals are converted into digital signals by A/D converter 20 and temporarily stored in memory (FIFO) 20. Then, the signals are beam-formed. The digital signals stored in memory 30 are delayed by delay controller 40, focused on a predetermined point and added together. The delay is continuously calculated so that the focal point moves along the depth direction. The added signals go through memory (FIFO) 50 and demodulator 60 and are displayed as an ultrasonic image on display device 70.
The delay profiles applied in a transmit-focusing and beam-forming are determined on the basis of the propagation velocity of the ultrasonic pulses in an object medium. That is, the delay profiles applied in the transmit-focusing and beaming forming are generated on the basis of the round-trip time that is required for the ultrasonic pulses to propagate and return. The propagation velocity of the transmitted ultrasonic pulses depends on the medium characteristics where the ultrasonic pulses propagate. For instance, when the medium is a human body, the propagation velocity of the ultrasonic is 1460 m/s at the grease, 1555 m/s at the liver, 1560 m/s at the blood, and 1600 m/s at the muscles.
Actually, the medium through which the ultrasonic pulses propagate is not uniform, and the propagation velocity can be changed along the depth of the medium. However, since the conventional transmit-focusing and beam-forming methods assume that the medium is uniform, they do not reflect the actual delay value that the ultrasonic pulses suffer as the medium changes. This results in errors of the transmit-focusing and the beam-forming.
As discussed above, the transmit-focusing and the beam-forming errors occur because the conventional ultrasonic imaging system assumes that the medium is uniform. Consequently, the image becomes distorted because of these errors. In order to solve this problem, it is necessary to use delay profiles that reflect the actual propagation velocity of the ultrasonic pulses on the basis of medium characteristics.
In order to beam-form scan-line data by applying a plurality of delay profiles, it is necessary to divide an object region to be ultrasonic imaged according to the medium characteristics. The present invention provides an ultrasonic system that divides the object region, determines the accuracy of the beam-forming by using a criterion, and generates scan-line data suitable for each of the divided areas.
To these objectives, a method of an adaptive beam-forming, in accordance with one aspect of the present invention comprises the steps of (a) transmit-focusing ultrasonic signals upon an object region to be ultrasonic imaged by means of a plurality of transducers; (b) receiving the ultrasonic signals reflected off said object region at said plurality of transducers, and beam-forming the received ultrasonic signals in accordance with associated delay profiles to obtain multiple sets of preliminary scan-line data; and (c) combining said multiple sets of preliminary scan-line data into scan-line data.
The combining step of the adaptive beam-forming method comprises the steps of: d. dividing said object region to be ultrasonic imaged into a plurality of determining areas; e. selecting one of said multiple sets of preliminary scan-line data in each of said determining areas divided in said step d; and f. combining said selected scan-line data to form an adaptive scan-line data.
A method of an adaptive transmit-focusing, in accordance with another aspect of the present invention, comprises the steps of: transmit-focusing a group of ultrasonic pulses based upon a plurality of delay profiles; and transmitting said transmit-focused group of ultrasonic pulses.
The step of transmit-focusing said group of ultrasonic pulses of the adaptive transmit-focusing method comprises, for generating each ultrasonic pulse of said group of ultrasonic pulses, the steps of: applying each of said plurality of delay profiles, the steps of; generating a plurality of waveforms from wave form data, each of said waveforms corresponding to each of said plurality of delay profiles; and multiplexing said generated plurality of waveforms.
According to the adaptive transmitting focusing and beam forming methods of the present invention, it is possible to reduce transmit-focusing and beam-forming errors generated from applying a single pattern of delay profile, and provide clear ultrasonic images.